This application is based on Japanese Patent Application No. 2000-175655, filed on Jun. 12, 2000, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to an oil pump unit for an engine, and more particularly to an improved oil pump unit that varies a volume of its own pumping chamber with rotation.
2. Description of Related Art
Relatively small watercraft such as, for example, personal watercraft have become very popular in recent years. This type of watercraft is quite sporting in nature and carries one or more riders. A hull of the watercraft typically defines a rider""s area above an engine compartment. An internal combustion engine powers a jet propulsion unit that propels the watercraft by discharging water rearwardly. The engine lies within the engine compartment in front of a tunnel which is formed on an underside of the hull. The jet propulsion unit is placed within the tunnel and includes an impeller that is driven by the engine.
Typically, the watercraft employs a lubrication system that lubricates portions of the engine. Some lubrication systems form a closed-loop. Such a lubrication system includes an oil tank containing lubricant oil, an oil pan forming a lower wall of a crankcase of the engine to which the lubricant oil that has lubricated the engine portions returns, a feed pump supplying the lubricant oil within the oil tank to the engine portions, and a scavenge pump returning the lubricant oil from the oil pan to the oil tank. Optionally, a trochoid pump construction is applied to the feed and scavenge pumps. Both of the pumps can be unitarily formed within a single housing. For example, respective pump assemblies can be disposed on a common shaft, which is journaled for rotation within the housing and driven by the engine, in series with each other.
In this arrangement, the housing has at least two inlet openings connected to respective inlet ports of the feed and scavenge pumps, and also at least two outlet openings connected to respective outlet ports of the feed and scavenge pumps. Generally, any side surfaces of the housing are available for forming the inlet and outlet openings. The pump unit occasionally is mounted on the engine body because the engine body normally defines both the engines portions which need lubrications and the oil pan therein.
One aspect of the present invention include the realization that a problem can arise with this arrangement when the pump housing is mounted directly to the engine body such that the internal passages on the housing are connected to internal oil passages in the engine body. In this arrangement, one of the pump which is disposed farther from the engine body than the other pump, necessarily has internal passages that connect the inlet and outlet ports of the pump to the inlet and outlet openings, respectively. The internal passages can produce flow resistance and the pumping ability of the pump is limited to the extent that is regulated by the flow resistance. A larger pump assembly may be useful under a certain engine speed, for example, less than 4,000 rpm to resolve the problem. However, such a larger pump assembly is no longer useful when the engine operates in a high speed range such as, for example, 4,000-7,000 rpm, because the lubricant oil is urged out from pumping chambers of the pump assembly immediately after being drawn into the chambers.
A need therefore exists for an oil pump unit for an engine that offers better performance over a broader range of engine speeds.
In accordance with one another aspect of the present invention, an oil pump unit for an internal combustion engine comprises a housing. A shaft extends within the housing and is journaled thereon for rotation about a shaft axis. The shaft is driven by the engine. An inner rotor is affixed to the shaft to rotate with the shaft. An outer rotor is disposed around the inner rotor to be rotated by the inner rotor. The inner and outer rotors together define at least one pumping chamber. A volume of the pumping chamber varies with the rotation of the inner and outer rotors. The inner rotor has first and second end portions spaced apart from each other along the shaft axis. The outer rotor has third and fourth end portions spaced apart from each other along the shaft axis. The housing defines a first inlet port and at least one outlet port at a location where the first end portion of the inner rotor and the third end portion of the outer rotor are positioned. The first inlet port and the outlet port selectively communicate with the pumping chamber with the rotation of the inner and outer rotors. The housing further defines at least a second inlet port at a location where the second end portion of the inner rotor and the fourth end portion of the outer rotor are positioned.
In accordance with another aspect of the present invention, an oil pump unit for an internal combustion engine comprises a housing. A shaft extends within the housing and is journaled thereon for rotation about a shaft axis. The shaft is driven by the engine. A first pump assembly is disposed on the shaft to be driven by the shaft. A second pump assembly is disposed on the shaft in series with the first pump assembly to be driven by the shaft. The first and second pump assemblies each defines end portions spaced apart from each other along the shaft axis. The housing defines a first inlet port and at least one outlet port at one of the end portions of the first pump assembly, a second inlet port and a second outlet port at one of the end portions of the second pump assembly, and at least a third inlet port at the other end portion of the second pump assembly.
In accordance with a further aspect of the present invention, a lubrication system for an internal combustion engine comprises a first oil reservoir arranged to contain lubricant oil. A second oil reservoir is arranged to receive the lubricant oil that has lubricated portions of the engine. An oil pump unit is arranged to supply the lubricant oil within the first oil reservoir to the portions of the engine and to return the lubricant oil within the second oil reservoir to the primary oil reservoir. The oil pump unit comprises a housing. A shaft extends within the housing and is journaled thereon for rotation about a shaft axis. The shaft is driven by the engine. A feed pump assembly is disposed on the shaft to be driven by the shaft. A scavenge pump assembly is disposed on the shaft in series with the feed pump assembly to be driven by the shaft. The feed and scavenge pump assemblies each defines end portions spaced apart from each other along the shaft axis. The housing defines a first inlet port and a first outlet port at one of the end portions of the feed pump assembly, a second inlet port and a second outlet port at one of the end portions of the scavenge pump assembly, and at least a third inlet port at the other end portion of the scavenge pump assembly.